As of currently, I'm not sure if this acheivement has been fixed, but to get it, host an online endurance game. Many on Steam are reporting that this isn't working as a cumlative achievement. Travel 100-120 blocks from start, and make sure to get enough iron or copper to make 28 metal blocks. Then dig deep enough into the ground to surround and protect yourself above, below, and the sides. MAKE SURE TO PLACE 1 TORCH above you. DO NOT PAUSE YOUR GAME, time counted won't count unless it's actively running. Now window out of the game and continue with your life. It will also get you the (working) cumulative, Survive Days, achievements.